1. Field of the Invention
This invention relates to a cross shaft joint (universal joint) used in a drive shaft portion or a steering device of a vehicle.
2. Related Art
A cross shaft joint has been used in a drive shaft portion or other portions of a vehicle, and such a cross shaft joint comprises a cross shaft member having four shaft portions arranged in a cross-shape, and bearing cups of a closed-bottom cylindrical shape angularly movably fitted respectively on the shaft portions through rolling elements (rollers). A grease nipple is provided at a central portion of this cross shaft member, and grease supplied via this grease nipple is distributed to oil holes formed axially in the respective shaft portions. On the other hand, a central recess (communicating with the oil hole in the shaft portion) and an outer peripheral recess (in which one ends of the rolling elements are disposed) are formed in an inner bottom face of each bearing cup, and this inner bottom face further includes an annular projected portion formed between the central recess and the outer peripheral recess and held in sliding contact with an end face of the shaft portion. Oil passageways (oil grooves) are formed in this annular projected portion, and grease supplied to the central recess from the oil hole is flowed to the outer peripheral recess via the oil passageways, and also these oil passageways serve to hold the grease at the annular projected portion.
The rolling elements roll between an outer peripheral surface of the shaft portion and an inner peripheral surface of the bearing cup, and the end face of the shaft portion and the inner bottom face of the bearing cup slide relative to each other, so that the friction therebetween becomes large, and seizure due to lack of lubrication becomes a problem. Therefore, in JP-A-55-24243 and JP-UM-A-55-36796 mentioned below, the shape and pattern of oil passageways in the annular projected portion are so designed as to prevent seizure, etc.
JP-A-55-24243 discloses radial oil passageways 227 formed in an annular projected portion 222 formed on an inner bottom face 219 of a bearing cup 205 as shown in FIG. 10A, and also discloses oil passageways 227 extending radially while curved in a circumferential direction as shown in FIG. 10B. JP-UM-A-55-36796 discloses an oil passageway 227 extending in a spiral shape as shown in FIG. 10C.
JP-A-2000-145806 discloses a technique in which a resin washer having oil passageways is interposed between an inner bottom face of a bearing cup and an end face of a shaft portion so as to prevent seizure.
With respect to the oil passageways 227 shown in FIG. 10A, when the bearing cup 205 angularly moves about the shaft portion reciprocally (i.e., in opposite directions) in accordance with a rotation of a shaft coupled to the cross shaft joint, grease tends to flow from a central recess 220 to an outer peripheral recess 221 via the oil passageways 227 at an initial stage under the influence of the centrifugal force. However, after a continuous use, the flow of the grease reaches saturation, so that fresh grease can hardly flow into the oil passageways 227, and the grease held in the oil passageways 227 is repeatedly used for lubricating the sliding surfaces. Therefore, the grease is gradually deteriorated, and the lubricating performance is lowered.
On the other hand, with respect to the oil passageways of FIG. 10B and the oil passageway of FIG. 10C, the flowing of the grease can be promoted to a certain degree by the reciprocal angular movement of the bearing cup 205. Namely, each oil passageway 227 is circumferentially inclined relative to the radial direction or circumferentially intersects the radial direction. Therefore, when the bearing cup 205 angularly moves, for example, in a direction of arrow A, the flowing of grease into each oil passageway 227 from an inner peripheral end 227a thereof is promoted, and when the bearing cup 205 angularly moves in the opposite direction B, the flowing of the grease into the oil passageway 227 from an outer peripheral end 227b thereof is promoted.
However, the bearing cup 205 is merely repeatedly angularly moved through a predetermined angle in the directions of arrow A and B, and therefore the grease moves reciprocally in and along the oil passageway 227, so that the grease resides in the oil passageway 227, and thus can not be properly circulated.